1. Technical Field
The field of the invention is electronic controllers for controlling industrial machines and processes, and more particularly processor-based circuit board modules used in such equipment and controllers.
2. Description of the Background Technology and Related Art
Industrial controllers are typically connected to assembly line equipment and process control equipment in manufacturing facilities and other industrial plants. Smaller controllers, including programmable controllers, have typically been built as a set of modules that are inserted in a rack somewhat like a set of books placed side-by-side in a bookcase. These modules may include a main processor (CPU) module, communication modules and I/O interface modules.
The main processor module (CPU) typically includes a microprocessor or microcomputer and a programmable read-only memory (PROM) for storing operating system instructions to be read and executed by the microprocessor. The module also had a random access memory (RAM) for storing data and application programs. Over the years the other modules have become peripheral processor modules with their own processor, PROM and RAM. These modules have been programmed to perform many specialized control functions under the general supervision of the main processor (CPU) module.
Where many different application programs are to be stored and executed, it is desirable to store and execute them in random access memory (RAM). This allows convenience in loading, testing and debugging such programs.
The invention herein relates to a specialized I/O module with a detachable RAM cartridge. Application programs can be developed in a higher-level language with off-line development systems and entered in the cartridge. When the program has been developed, the cartridge may then be carried to a certain location in a factory and installed in the processor-based module in a programmable controller system.
In such an arrangement, there is a need to prevent the processor from writing data to locations in the RAM, except when the processor is actually executing the application program. This helps assure the integrity of the program, which may then be readily reproduced where it is desired to use it in another machine or provide a duplicate cartridge. Thus, when background operations are being executed, the RAM program memory is inaccessible or "locked out" against access by its associated processor.